(a) Field of the Invention
This invention relates to a preparation process of desulfurizing and denitrating agents for an off-gas produced upon combustion of a fuel such as coal or heavy oil.
(b) Description of the Prior Art
Sulfur oxides, nitrogen oxides and other noxious gases, which are contained in an off-gas produced upon combustion of coal, heavy oil or other fuels, have been found to cause damage to buildings and structures and moreover to have an extremely serious effect not only on animals and plants but also on humans. Research has been conducted on the removal of the above-described materials from off-gases by means of desulfurization and denitration, leading to the development of various processes.
These desulfurization and/or denitration processes may be roughly divided into dry-type processes and wet-type processes. As dry-type desulfurization processes to which the present invention pertain, there have been known those shown in Table 1.
TABLE 1 __________________________________________________________________________ Dry-Type Off-Gas Desulfurization Processes* Manner of Process Reaction Reaction Recovered treatment feature Reactants Process name temp. product material __________________________________________________________________________ Absorption Reacted with Activated Activated manga- 130.degree. C. MnSO.sub.4 Ammonium a metal manganese nese oxide process sulfate oxide to oxide form sulfate Alkalized Alkalized alumina 280- Na.sub.2 SO.sub.4 Sulfur alumina process 360.degree. C. Limestone, Lime blowing 500- CaSO.sub.4, Mixture of slaked lime process 1200.degree. C. etc. unreacted lime dolomite or oxide and dolomite gypsum hydroxide Adsorption Adsorption of (Adsorbent) Activated carbon 100.degree. C. H.sub.2 SO.sub.4 Sulfuric acid SO.sub.2 with an Activated process adsorbent carbon Reinluft process 100.degree. C. SO.sub.2 Sulfur Catalytic Oxidation of (Catalyst) Benelec process 420- SO.sub.3 Sulfuric acid oxidation SO.sub.2 into SO.sub.3 Vanadium- (for coal boilers) 480.degree. C. by a catalyst base TIT-Kiyoura 220- (NH.sub.4).sub.2 SO.sub.4 Ammonium sulfate, catalyst process 260.degree. C. sulfuric acid __________________________________________________________________________ *Cited from the following publication: "Smoke and Soot Control Technology Series, No. 7 Smoke and Soot Control Technology for Electric Power Industry", Government of Japan, Ministry of Industrial Science and Technology, Enterprise Bureau and Public Benefit Utilities Bureau, (1969).
The above-described conventional dry-type desulfurization processes however involve a variety of problems. In the absorption processes shown in Table 1, it is required, for example, to use costly NH.sub.3 (the activated manganese oxide process) or a valuable reducing gas (the alkalized alumina process) for the regeneration of the reactants (and for the recovery of sulfur or sulfur compounds) or to employ a high reaction temperature (the alkalized alumina and lime blowing processes). The adsorption processes are accompanied by such drawbacks as having to use expensive activated carbon, which is susceptible to deterioration. In the catalytic oxidation processes, it is necessary to use expensive vanadium-base catalysts, which, moreover, are liable to deterioration, and relatively-high reaction temperatures are required.
It is the catalytic reduction process making use of ammonia that is widely used as a dry-type denitration process. This process is however accompanied by such problems as having to rely upon an expensive catalyst and having a high running cost because ammonia is oxidized by nitrogen gas and hence consumed completely.
Further, no practical process which permits simultaneous execution of desulfurization and denitration in a dry state has materialized.